Many knee problems can be diagnosed from the story of the initiating incident together with a competent examination.

Usually those additional special investigations - such as X-ray and MRI scan - serve only to confirm what is already suspected.

With the advent of the internet, people with medical problems find themselves turning more and more to this medium to get an idea of what their problem is, before they approach their doctor. However, it can be a confusing place for the beginner until they get an idea of the range ofdisorders into which their symptoms might slot.

This list will offer some pointers to help people with their researching, 'sign-posting' them to likely possibilities without being proscriptive about exactly what their diagnosis is.

"Common things occur commonly"

A common maxim in medicine is that 'common things occur commonly'. It may be that your own disorder is uncommon and not listed here, but these lists refer to common knee problems and symptoms.

At the very least, you should have some idea of the proper terminology which is so important when you are researching online. There is nothing more frustrating than trying to find out more about your own medical problem when you have no idea of the correct words to put into the search bar.


One of the first questions that a knee surgeon or physiotherapist might ask at your first consultation is "Did you have an injury?"

This is generally the case irrespective of those symptoms that you are experiencing. The kinds of problems that follow an injury are generally very different from those that come on without any precipitating incident.


Knee Pain

Knee pain coming on after injury -

  • if the knee pain was agonising initially after the injury and is continuing, there is marked 'doughy' swelling and you are unable to bear weight, then it might be that there is a 'fracture' (bone break). There are many different kinds of fractures that can occur in the knee - for example, a fall onto the kneecap may split it in two or even shatter the bone into pieces (patellar fracture). Another rather common but important fracture is a'tibial plateau fracture', which you might sustain if you were running and the foot caught in a hole but the body carried on with the momentum.
  • if the knee pain was agonising initially after injury, was associated with a loud 'pop' and marked 'balloon-like' swelling, but the pain tended to ease later, then it may be that there is a 'ligament tear', for example a cruciate ligament, and particularly an anterior cruciate ligament (or ACL). In this case the knee may feel extremely unstable although you may be able to bear weight with difficulty.
  • if the knee pain was severe initially after injury, with continuing pain and marked tenderness in the joint line, then this might indicate a torn collateral ligament or a torn meniscus (the shock absorber in the knee). A torn meniscus may also be associated with swelling, but this may come on more gradually than with a cruciate ligament tear.

Knee pain coming on without injury -

When there has been no injury the person may not be altogether sure about when and how the pain began. Of course there are many possible sites and causes of knee pain coming on without injury - muscle or tendon sprain,inflammatory conditions, arthritic conditions - but these are the commononest.

  • intermittent pain around or behind the kneecap, exacerbated by exercise on uneven ground or going up or down stairs - this might be 'anterior knee pain', a catch-all name for several conditions that may be stressing the kneecap (eg mal-tracking, tilt). The situation is commonly 'functional', that is the quadriceps and hamstrings muscles are insufficiently strong, there may be weakness of the lower back and pelvic muscles, or the ankles or feet may result in a rolling over of the foot. Unfortunately many patients in this group submit to surgical'correction' when competent rehabilitation and footwear might have resolved the situation.
  • diffuse ill-defined nagging pain around the front of the knee, which maybe worse at night, could actually not be coming from the knee at all but from the hip - what we called 'referred' pain - although knee arthritis will give similar symptoms and it may take X-rays to differentiate between them.
  • persistent burning pain at back of knee particularly after unusual amounts of exercise may be due to a 'Baker's cyst', a fluid-filled swelling which communicates with the interior of the knee joint and reflects an increased pressure of fluid in the knee joint as well.
  • chronic distressing pain below the kneecap in the tendon region, exacerbated by jumping exercise such as volleyball, basketball and tennis, might indicate a condition known as patellar tendinosis, which seems to be a degenerative condition of the tendon and challenging to treat.
  • pain at the outer side of the knee after unusual or excessive running or walking may be due to an overuse problem called 'ilio-tibial band syndrome'.
  • pain on the inner aspect of the knee but below the joint line, in both sporting and sedentary populations, may be due to 'pes anserinus bursitis', a largely self-limiting inflammatory condition.
  • intermittent attacks of sudden very severe knee pain, with swelling and redness, may be a symptom of gout.

I think you can see from this that the cause of knee pain has to be teased out with careful questioning and examination, as there are many separate structures that may be giving rise to the pain.


Knee Noises

The knee can make several kinds of noises - some are important and some are not of much consequence - but patients obviously imagine that something serious is going on.

Knee noises at the time of injury -

  • an audible 'pop!' at the time of injury, followed by marked pain and swelling, suggests a cruciate ligament or a meniscus tear.
  • a loud 'crack! with very severe pain, and inability to walk, often with marked but boggy swelling, might be due to a 'fracture' (bone break)
  • Most often knee noises are less dramatic, and if you put your hand on your knee you can also 'feel' the noise. These noises may not be there all the time but may come on when the knee has been stressed, perhaps by some uncommon activity. Sometimes they are heard only in response to certain activities such as going down stairs or squatting.

Knee noises during ordinary activities -

  • a very common kind of noise is called 'crepitus', and I liken it to the sound that would be made if you crunch Rice Krispie breakfast cereal in your hand. A similar noise is that made if you rub some of your hair just near your ear between your finger and thumb. This crackly noise can also be felt if you lay your hand over the knee while moving the joint.
  • a pop when the knee gets to a certain position, preceded by an uncomfortable feeling, may be due to an old meniscus tear or a discoid meniscus' - but also examination may not reveal the cause of the noise,and it may be put down to 'normal'.
  • a little palpable, and sometimes audible, snap on the inner aspect of the knee on straightening the knee, may be due to a medial plica, a fold of joint lining that can bowstring over the rounded end of the femur bone.



To understand knee swelling, you need to know a little bit about the anatomy of the knee. Surrounding the joint cavity is a waterproof capsule,which can become like a balloon if the cavity fills suddenly with blood from a torn blood vessel. Then in addition, outside of this main cavity are several little waterproof envelopes called 'bursae', which normally are flattened and help to facilitate movement of the various tissues over one another when the knee moves. If one is damaged, then it can fill with fluid - either clear fluid secreted into the joint or even blood, and sometimes these can become infected. The common one everyone knows about is 'housemaid's knee',where the bursa in front of the kneecap gets traumatised by kneeling. Bursa swelling is very discrete - like a little ball - and can look really odd. Finally,there may be swelling in the tissues around the knee if the capsule has been torn, and this kind of diffuse swelling has a boggy look and feel.

Knee swelling immediately after injury -

  • if extensive, tense, painful - there could be 'blood in the joint (haemarthrosis), with internal damage' - this can occur from a torn cruciate ligament, or a torn meniscus (particularly if torn around the outer edge). It can also occur after knee surgery of course.
  • if localised, tense, painful, the swelling could be a bursa inflammation or bleed, and this usually follows unusual repetitive trauma to the knee,such as after laying a carpet.

Knee swelling without any definite injury -

  • if severe, painful - think 'rheumatoid condition or infection' (an emergency).
  • if persistent - it could be 'internal damage or arthritis'.
  • if recurrent - think 'rheumatoid condition'


Knee Instability

Instability of the knee implies that it cannot be trusted. The whole joint may feel unstable so much so that stepping off the kerb can be frightening, or the kneecap may be unstable, jumping out of its underlying groove. I am going to put into this group also loose structures that can catch inside the joint.

  • Catching - You may be walking along quite happily when something 'catches' painfully right inside the joint. This may be a loose piece of joint cartilage or meniscus,or a plica, which suddenly gets caught between the bones. A loose piece of cartilage would be called a 'loose body'.
  • Giving way - Giving way is similar to catching, but the sudden incident causes the muscles to be briefly inhibited and the knee collapses.
  • Locking - Locking is when the knee cannot fully straighten because there is something in the joint which is temporarily preventing this. The common cause is a longitudinal tear in a meniscus - it can be from a new injury or an old one - and a sliver of meniscus gets flipped over to the wrong side of the rounded end of the femur. It may unlock on its own or it may require help from a surgeon, possibly under sedation or anaesthesia. This kind of tear is called a 'bucket-handle' tear.
  • Subluxing - This is specifically referring to the kneecap, where it partially de-rails but then it returns to the groove in which it normally lies. It may happen occasionally or may be habitual.

    The cause may be related to an injury with damage to the ligaments that usually stabilise the knee, or there may be a structural abnormality of the kneecap or its underlying groove.
  • Dislocating - In this context I am referring to a dislocation of the kneecap, where it jumps right out of the groove and does not return by itself but requires intervention.The term dislocation can also refer to a catastrophic disruption of the knee ligaments holding the long bones together, but that is not something for a little primer like this.

    Dislocation of the kneecap can happen just once, or it can become recurrent, and the causes are the same as with subluxation. In particular a structural abnormality of the groove - trochlear dysplasia - needs to be considered, as well as the alignment and possible rotational abnormality of the long bones.